We know, that photon change direction for 1.75'', when it flies close to the sun. This angle is proportional to radius of the sun. If we calculate clasically the angle is 0.82'' (arc second). Which is momentum, which is given to sun (or black hole) by the photon change of direction. Is the same as change of momentum of the photon. Must we calculate change of momenum of the photon clasicaly or relativistically?